Cell Division and Mitosis

1. Cell Division and Mitosis Chapter 9

2. 9.1 Dividing Cells Eukaryotic organisms • Mitosis • Meiosis Prokaryotic organisms • Prokaryotic fission

3. Roles of Mitosis • Multicelled organisms • Growth • Cell replacement • Some protistans, fungi, plants, animals • Asexual reproduction

4. Chromosome • A DNA molecule & attached proteins • Duplicated in preparation for mitosis one chromosome (unduplicated) one chromosome (duplicated)

5. Chromosome Number • Sum total of chromosomes in a cell • Somatic cells • Chromosome number is diploid (2n) • Two of each type of chromosome • Gametes • Chromosome number is haploid (n) • One of each chromosome type

6. Human Chromosome Number • Diploid chromosome number (n) = 46 • Two sets of 23 chromosomes each • One set from father • One set from mother • Mitosis produces cells with 46 chromosomes--two of each type

7. Organization of Chromosomes DNA one nucleosome DNA and proteins arranged as cylindrical fiber histone Figure 9.2Page 153

8. 9.2 The Cell Cycle interphase G1 S telophase anaphase Mitosis G2 metaphase prophase Figure 9.4Page 154

9. Interphase • Usually longest part of the cycle • Cell increases in mass • Number of cytoplasmic components doubles • DNA is duplicated

10. Mitosis • Period of nuclear division • Usually followed by cytoplasmic division • Four stages: Prophase Metaphase Anaphase Telophase

11. Control of the Cycle • Once S begins, the cycle automatically runs through G2 and mitosis • The cycle has a built-in molecular brake in G1 • Cancer involves a loss of control over the cycle, malfunction of the “brakes”

12. Stopping the Cycle • Some cells normally stop in interphase • Neurons in human brain • Arrested cells do not divide • Adverse conditions can stop cycle • Nutrient-deprived amoebas get stuck in interphase

13. The Spindle Apparatus • Consists of two distinct sets of microtubules • Each set extends from one of the cell poles • Two sets overlap at spindle equator • Moves chromosomes during mitosis

14. Spindle Apparatus one spindle pole one of the condensed chromosomes spindle equator microtubules organized as a spindle apparatus one spindle pole Figure 9.5Page 155

15. chromosome (unduplicated) in cell at interphase same chromosome (duplicated) in interphase prior to mitosis mitosis, cytoplasmic division chromosome (unduplicated) in daughter cell at interphase chromosome (unduplicated) in daughter cell at interphase Maintaining Chromosome Number Stepped Art Figure 9.6Page 155

16. 9.3 Stages of Mitosis Prophase Metaphase Anaphase Telophase

17. Early Prophase - Mitosis Begins Duplicated chromosomes begin to condense Figure 9.7 Page 156

18. Late Prophase • New microtubules are assembled • One centriole pair is moved toward opposite pole of spindle • Nuclear envelope starts to break up Figure 9.7 Page 156

19. Transition to Metaphase • Spindle forms • Spindle microtubules become attached to the two sister chromatids of each chromosome Figure 9.7 Page 156

20. Metaphase • All chromosomes are lined up at the spindle equator • Chromosomes are maximally condensed Figure 9.7 Page 156

21. Anaphase • Sister chromatids of each chromosome are pulled apart • Once separated, each chromatid is a chromosome Figure 9.7 Page 156

22. Telophase • Chromosomes decondense • Two nuclear membranes form, one around each set of unduplicated chromosomes Figure 9.7 Page 156

23. Results of Mitosis • Two daughter nuclei • Each with same chromosome number as parent cell • Chromosomes in unduplicated form Figure 9.7 Page 156

24. 9.4 Cytoplasmic Division • Usually occurs between late anaphase and end of telophase • Two mechanisms • Cell plate formation (plants) • Cleavage (animals)

25. Cell Plate Formation Figure 9.8Page 158

26. Animal Cell Division Figure 9.9Page 159